The present invention relates to an improved process for the polymerization of alpha-olefins. It also relates to solid catalyst complexes which can be used for the polymerization of alpha-olefins and to a process for preparing these complexes.
For the low pressure polymerization of olefins, it is known to use catalyst systems comprising a transition metal compound and an organometallic compound.
Catalyst systems in which one constituent is obtained by reacting together:
(1) an organic oxygen-containing metal compound or a metal halide, such as magnesium ethanolate or magnesium dichloride,
(2) an organic oxygen-containing transition metal compound, such as titanium tetrabutylate, and
(3) an aluminum halide, such as ethylaluminum dichloride are also known from Belgian Pat. Nos. 791,676, filed on Nov. 21, 1972 (corresponding to U.S. Pat. No. 3,901,863), and 799,977, filed on May 24, 1973 (corresponding to German Application No. 23 24 776) in the name of Solvay & Cie.
These catalyst systems are unique in the extremely important advantages which they exhibit. Thus, their activity and their productivity are very high. Their preparation is extremely simple and does not give rise to any pollutant by-product. Finally, the morphology of the polymer obtained permits continuous suspension polymerization using a very high relative proportion of polymer and therefore a very low relative amount of diluent to be treated before recycling.
However, the use of catalyst systems such as that described above also presents a serious disadvantage when they are used in a process in which the polymer is obtained directly in the form of particles. In fact, it has been found that, although of uniform particle size distribution, the polymers obtained directly as particles under the action of such catalyst systems contain a relatively high percentage of fine particles and have a relatively small average particle size.
The morphology of the particles of these polymers consequently presents problems during their drying, their storage, their transportation, their handling and their use in the known molding techniques. The attempts which have hitherto been made to increase the mean particle size of the polymers obtained directly by polymerization using the catalyst systems described above have not been completely successful. Thus, it has been found that a certain increase in the average diameter of the particles can be achieved by raising the temperature at which the aluminum halide is employed. However, this increase in the average diameter is unfortunately accompanied by a decrease in the apparent specific gravity and a substantial broadening of the particle size distribution.